1. Field of the Invention
This invention relates generally to the field of optical and medical devices, and more specifically to an apparatus and method for microarray implementation for the detection of multiple analytes such as chemical agents and biological molecules using photonic crystals.
2. Background of the Invention
Label-free optical sensors based on photonic crystals have been demonstrated as a highly sensitive potential method for performing a large range of biochemical and cell-based assays. For background information on photonic crystals, the reader is directed to Joannopoulos, J. D., R. D. Meade, and J. N. Winn, Photonic Crystals, 1995 Princeton, N.J.: Princeton University Press. Tight confinement of the optical field in photonic crystal microcavities leads to a strong interaction with the surrounding ambient in the vicinity of the microcavity, thereby leading to large sensitivity to changes in refractive index of the ambient. Much of the research in photonic crystal devices has relied on enhancing refractive index sensitivity to a single analyte (Lee M. R., Fauchet M., “Nanoscale microcavity sensor for single particle detection,” Optics Letters 32, 3284 (2007)). Research on photonic crystals for multiple analyte sensing has focused on one-dimensional photonic crystal grating-like structures (see patents US20080225293 and US20030027328) that measure the resonant peak reflected wavelengths; such sensors have wide linewidths of the resonant peaks due to one-dimensional confinement and do not utilize the full potential of narrow resonant linewidths of two-dimensional photonic crystal microcavities. Furthermore, measurements are made from each sensor element in the array in a serial process, requiring multiple sources and detectors for parallel sensing beyond a single element. Research has been performed with one-dimensional photonic crystal microcavities coupled to ridge waveguides (See Mandal S. and Erickson D., “Nanoscale optofluidic sensor arrays”, Optics Express 16, 1623 (2008)). One dimensional photonic crystal microcavities, in addition to poor optical confinement, do not utilize the slow light effect due to reduced group velocity in two-dimensional photonic crystal waveguides that would otherwise enhance coupling efficiency and thereby improve signal-to-noise ratio of sensing. Demonstrated two dimensional photonic crystal waveguide biosensors rely on shifts of the stop-gap (see Skivesen N. et al., “Photonic crystal waveguide biosensor”, Optics Express 15, 3169 (2007)) or shifts of the resonant peak of an isolated microcavity (see Chakravarty S. et al., “Ion detection with photonic crystal microcavities”, Optics Letters 30, 2578 (2005)). In either case, the design is not suitable for the fabrication of microarrays for multiple analyte sensing.
Two dimensional photonic crystal microcavities integrated with two-dimensional photonic crystal waveguides offer the possibility of integrating the high quality-factor resonances of two-dimensional photonic crystal microcavities with the slow light effect of two-dimensional photonic crystal waveguides for high sensitivity, high signal-to-noise ratio sensing. Furthermore, multiple photonic crystal microcavities can be simultaneously arrayed along a single photonic crystal waveguide, so that a single measurement can be performed in parallel to elicit the response from multiple sensor elements, thereby increasing measurement throughput and reducing cost. An array of two sensors demonstrated using two-dimensional photonic crystal microcavities uses multiple ridge waveguides between individual photonic crystal microcavities. Coupling between photonic crystal waveguides and ridge waveguides introduces additional significant transmission loss at each interface, thereby significantly reducing signal-to-noise ratio as each microcavity is added for multiple sensing. The design demonstrated by Guillermain et al. (see Guillermain E., Fauchet P. M., “Multi-channel sensing with resonant microcavities coupled to a photonic crystal waveguide,” JWA 45, CLEO Conference (2009)) in effect employs multiple photonic crystal waveguides and also employs microcavities with significantly poor quality factors that make the designs unsuitable for high sensitivity sensing. Better designs are needed in the art to realize photonic crystal microarray devices that efficiently couple light from ridge waveguides to a single photonic crystal waveguide, wherein multiple photonic crystal microcavities with high quality factors and covering a large bandwidth for sensing are coupled to a single photonic crystal waveguide for high sensitivity multiple sensing.
A standard on-chip multiple protein patterning technique using lithography typically requires a pre-bake resist temperature of 100° C. or higher. At the very least, temperatures this high compromise or alter biological functionality, and at the very worst they may destroy its function. Most proteins are stable in vivo at a temperature of 37° C., but this stability is dependent on chaperone proteins that maintain the proper conformation of other proteins in cells. Since proteins in vitro lack these chaperone proteins, they must be maintained at even lower temperatures to prevent denaturation and loss of function. Designs are needed to enable patterning of different kinds of biomolecules in aqueous phase to preserve functionality of biomolecules.
Designs are needed in the art to integrate two-dimensional photonic crystal microcavities with two-dimensional photonic crystal waveguides for multiple analyte sensing and designs are further needed to pattern multiple biomolecules, of different constitutions, on the photonic crystal substrate while preserving their functionality.